Horizontal wind tunnels have, for over a century, been used to study the flow of air around objects; particularly flying objects. As early as 1901, Orville and Wilbur Wright anchored miniaturized wing profiles in a horizontal tube and exposed them to airflows, to study their airfoil characteristics, drag force and lift force. This simple method to simulate flight without actually flying has played a central role in the development of modern aircraft and other devices exposed to airflows. Modern horizontal wind tunnels typically have a closed tunnel circuit, recirculating air propelled by a fan system. The recirculation has advantages such as conserving energy and minimizing noise emissions outside the tunnel. In fast-flow operations, a cooling system is needed since the recirculating air maintains energy and therefore gradually rises in temperature. Typically, the recirculating wind tunnel system is designed as a circuit of rectangular shape with 90 degree corners. The part of the wind tunnel used for study, usually called the “test section”, is considered to be dimensioning of the entire tunnel system, the main parameters being duct width (W) and length (L). In modern recirculating tunnel systems, the test section is preceded by a contraction section, reducing cross sectional area by a factor in the range of 4-9 in order to produce a high flow rate with high quality (low turbulent intensity and length scale) in the test section, and is usually followed by a first expanding duct section, two 90 degree turns, a fan system, and additional expansion ducts and two 90 degree turns returning to the contraction section. The reason for this system design is a combination of several factors, including aerodynamic efficiency and flow quality in the test section. All in all, the effect of the system design limitations of modern horizontal wind tunnels is that they become very large and very heavy (in the order of 25-50 meters long and tens to hundreds of metric tons in weight), if they are to harbor high flow rates with good quality in a large test section capable of encompassing objects in the size of human bodies.
Another type of wind tunnel, in which the objects are not anchored but float freely, is the vertical wind tunnel, used today mostly for skydiving simulation. By blowing air directly opposite to the direction of the gravitational acceleration, e.g. vertically upwards, a state of force equilibrium may be reached at which an object or person is floating on the cushion of the vertically ascending air current. For this purpose, the vertical rather than the horizontal wind tunnel is suitable, since objects in a vertical wind tunnel cannot fly; an object that starts flying in a vertical wind tunnel will, because of its forward momentum, immediately hit the wall. One could say that a horizontal wind tunnel is suitable for simulating flight without permitting the studied objects to fly freely (this would require active propulsion inside the tunnel with, for example, a propeller or jet engine), and a vertical wind tunnel is suitable for allowing objects to float freely without flying.
The U.S. Pat. No. 7,156,744 B2 “Recirculating Vertical Wind Tunnel skydiving simulator” describes a state-of-the-art vertical wind tunnel technology for keeping people floating on a cushion of air. Several other patents describe various vertical wind tunnel designs for sports and recreational purposes, indicating great business value and public interest in this type of recreational device for sport and experience based consumption. The vertical wind tunnel has been an important development in these kinds of sports, but now appears limited by its vertical walls, which like a cage prevents flying for real. In this sports population, it would be desirable with a wind tunnel apparatus that overcomes this limitation and creates conditions for people to experience actual flight, indoors.
Typically, a vertical sports wind tunnel may be circa 30 m high. In an optimal wind tunnel, a test section with a diameter of 4 m would require a height of 54 m, but the designers and manufacturers of vertical sports wind tunnels have tried various technological workarounds to slightly decrease this value, since building permits for such large edifices are difficult to obtain. It is often desirable to place a sports and recreation venue accessible to customers, such as in a shopping mall or close to other sports and recreation venues, but this is difficult if the basic design is a very high tower.
There is therefore clearly a need for improved wind tunnels where human flight can be achieved and it is a benefit if the required height dimension of the tunnel system is smaller than today's vertical sports tunnels. For any type of wind tunnel for human use, a safety system for allowing safe use of the wind tunnel is also needed so that the risk of injury can be kept to a minimum. Previously known safety systems for vertical wind tunnels generally consist of at least one strap or handle fastened to a harness or clothing worn by a person using the tunnel and hand-held by an instructor or other safety personnel. The prior-art safety systems are both costly by requiring a safety instructor for each flyer, less safe, by involving a human as an anchor point, and limiting in the possible movements that can be performed by the person using the tunnel.
The US U.S. Pat. No. 3,276,251 “Test unit free flight suspension system” describes a state-of-the-art wind tunnel technology for keeping aircraft models suspended within a wind tunnel test section. Several other patents, such as U.S. Pat. No. 1,947,962 “Aeronautic training apparatus” describe various designs of suspension systems for use in wind tunnel systems. However, none of these are suitable for use as a safety system for human flyers in an inclined wind tunnel, since no prior art describes a technology permitting the full range of three-dimensional movements desired combined with the strict delimiting properties desired, preventing said flyer from leaving the test section or colliding with its inner structures.